Prior art which is related to this technical field can e.g. be found in technical specifications according to 3GPP TS 36.321 (e.g. version 11.2.0), 3GPP TS 36.331 (e.g. version 11.3.0), 3GPP TS 36.300 (e.g. version 11.5.0) and 3GPP TS 36.101 (e.g. version 11.4.0).
The following meanings for the abbreviations used in this specification apply:
APE: application processor engine
BB: baseband
BS: base station
CA: carrier aggregation
CC: component carrier
CLTD: closed loop transmit diversity
CPC: continuous packet continuity
CPU: central processing unit
DCO: digitally controlled oscillator
DL: downlink
DRX: discontinuous reception
DSDA: dual SIM (subscriber identification module) dual active
DTX: discontinuous transmission
eNB: evolved node B
EUTRA: evolved universal terrestrial radio access
FDD: frequency division duplex
FE: front end
HB: higher band
HW: hardware
IC: integrated circuit
ID: identification
IL: insertion loss
LA: local area
LAeNB: LA eNB (eNB controlling LA cell)
LB: lower band
LNA: low noise amplifier
LO: local oscillator
LTE: Long Term Evolution
LTE-A: LTE Advanced
MAC: medium access control
MIMO: multiple input multiple output
MUX: multiplexer, multiplexing
PA: power amplifier
PCC: primary component carrier
Pcell: primary cell
PLL: phase locked loop
RAT: radio access technology
RF: radio frequency
RFIC: radio frequency integrated circuit
RX: receiver, reception
SCC: secondary component carrier
Scell: secondary cell
TPC: transmission power control
TX: transmitter, transmission
VCO: voltage controlled oscillator
UE: user equipment
UL: uplink
In the last years, an increasing extension of communication networks, e.g. of wire based communication networks, such as the Integrated Services Digital Network (ISDN), DSL, or wireless communication networks, such as the cdma2000 (code division multiple access) system, cellular 3rd generation (3G) communication networks like the Universal Mobile Telecommunications System (UMTS), enhanced communication networks based e.g. on LTE, cellular 2nd generation (2G) communication networks like the Global System for Mobile communications (GSM), the General Packet Radio System (GPRS), the Enhanced Data Rates for Global Evolutions (EDGE), or other wireless communication system, such as the Wireless Local Area Network (WLAN), Bluetooth or Worldwide Interoperability for Microwave Access (WiMAX), took place all over the world. Various organizations, such as the 3rd Generation Partnership Project (3GPP), Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN), the International Telecommunication Union (ITU), 3rd Generation Partnership Project 2 (3GPP2), Internet Engineering Task Force (IETF), the IEEE (Institute of Electrical and Electronics Engineers), the WiMAX Forum and the like are working on standards for telecommunication network and access environments.
A new development of communication network systems is the implementation of heterogeneous networks consisting of e.g. a “normal” communication cell (referred to as macro cell) and plural small cells (referred to as Scells or local area (LA) cells) which allow a better coverage and possibly outsourcing options for communications conducted in the macro cell.
In carrier aggregation (CA), it is intended to increase communication data throughput by using simultaneous communication link with multiple carrier components (CC). For example, CA is done in DL direction with secondary CC (SCC). SCC may use an adjacent or non-adjacent frequency band with regard to the PCC. For example, an adjacent CC is related to a so-called intra-band CA case, while a non-adjacent CC may be related to a so-called inter-band CA (but is also usable in an intra-band CA). In addition, CC's can include several clusters that in practice mean that RB's in one CC can be allocated in non-contiguous manner. Also UL CA is considered for increasing data throughput further, e.g. in connection with relays or routers.
In protocol point of view, DL CA communication creation starts from an active primary cell (Pcell) communication link, which is always used for UL communication purposes in combination with DL CA. DL communication link/s from one or more secondary cell/s are then configured according to allocated radio resources. It is to be noted that prior to a Scell communication link establishment, a communication unit such as a UE using the CA communication may conduct Scell measurements and report results to a communication counterpart (e.g. the eNB). Furthermore, a Scell communication link may be disconnected after some period, e.g. when the UE detects that a Scell timer or the like in the UE reaches a limit which may be a value being predefined by the network.
When the UE is attached to the network, a so-called handover may take place e.g. due to mobility or load reasons. In such a handover, the Scell communication link is not kept active. The handover is executed from one Pcell communication resource (e.g. one eNB) to an alternate Pcell communication resource (e.g. another eNB) according to known handover procedures. In this situation, a new DL CA communication (with Scells) will be established as indicated above.